The present invention relates to an image recording apparatus, and more particularly, to an image recording apparatus capable of recording a visible image on a predetermined recording medium by using a recording head having a plurality of recording elements.
One of such apparatuses is an ink-jet type printer. In such a printer, the space between nozzles of the recording head has been reduced, and thus resolution of 300 dpi through 400 dpi is possible.
For example, a recording head having a length corresponding to the shorter side of an A4 paper (approximately 21 cm), so-called a full-multi-head, includes approximately 3,000 nozzles.
In this case, if all the nozzles are simultaneously driven, a large amount of electric power is required, resulting in increase in cost and size of apparatus. Therefore, the nozzles are generally divided into a plurality of groups and driven in group units.
FIG. 2 is a diagram showing an example of a full-multi-type recording head having ink-discharge ports arranged over the width (shorter side) of a recording medium. As shown in FIG. 2, electrothermal transducing elements 1 are formed on a substrate such as silicon at regular intervals by the same manufacturing process as that used in semiconductor. These elements are connected to electric wires (not shown) respectively. Partitions 14 are formed by building resin layers between the elements 1, and a fluid passageway forming member 16 in the form of a plate is adhered to the top of the partitions 14. The member 16 is further adhered to a glass plate 17, thus discharge ports 12, fluid passageways 13, and a common fluid chamber 15 are formed.
FIG. 10 is a diagram illustrating a general circuit of a drive control circuit which drives a recording head shown in FIG. 2.
In FIG. 10, R.sub.1-1 .about.R.sub.1-n, R.sub.2-1 .about.R.sub.2-n, . . . R.sub.m-1 .about.R.sub.m-n are electrothermal energy transducing elements (hereinafter referred to as "recording elements"). As shown in FIG. 10, n recording elements comprise a single group, and m groups of recording elements comprise a recording head.
During image recording, data expressed by bit is synchronized with a data transfer clock SCLK and transferred to shift registers 2-1.about.2-m. The number of bits of the data is the same as that of all the recording elements. When all the data is transferred, latch circuits 1-1.about.1-m respectively latch the data stored in the shift registers 2-1.about.2-m.
Subsequently, if the first group receives a pulse signal (drive signal BE.sub.0), from a CPU (not shown), whose signal level is high for a predetermined period of time, the corresponding recording elements R.sub.1-1 .about.R.sub.1-n are heated in accordance with the data held in the latch circuit 1-1. As a result, the nozzles of the heated recording elements discharge an ink-droplet.
Subsequently, the recording elements in each group are driven when the CPU (not shown) sequentially outputs drive signals BE.sub.1 .about.BE.sub.m.
It is assumed that multi-valued image is recorded by discharging an ink droplet from the same nozzle for plural times. In this case, it is required that data is transferred for the number of times corresponding to the density of a pixel to be recorded. Accordingly, as the level value of an image to be reproduced increases, it takes more time to transfer data, thus resulting in decrease of recording speed.
The CPU which transfers data in particular performs an image development processing and other various processings for, e.g., a memory (not shown). Accordingly, if the above-described data transfer is frequently performed, the time divided for processings other than the data transfer is reduced. As a result, printing speed is decreased.
Furthermore, in a case where an image is recorded in three levels, a driving signal is outputted for 2.times.m times. Thus the load on the CPU increases.